The tools/testing/selftests/bpf test program test_dev_cgroup fails with the following error when compiled with llvm 6.0. (I did not try with earlier versions.) libbpf: load bpf program failed: Permission denied libbpf: -- BEGIN DUMP LOG --- libbpf: 0: (61) r2 = *(u32 *)(r1 +4) 1: (b7) r0 = 0 2: (55) if r2 != 0x1 goto pc+8 R0=inv0 R1=ctx(id=0,off=0,imm=0) R2=inv1 R10=fp0 3: (69) r2 = *(u16 *)(r1 +0) invalid bpf_context access off=0 size=2 ... The culprit is the following statement in dev_cgroup.c: short type = ctx->access_type & 0xFFFF; This code is typical as the ctx->access_type is assigned as below in kernel/bpf/cgroup.c: struct bpf_cgroup_dev_ctx ctx = { .access_type = (access << 16) | dev_type, .major = major, .minor = minor, }; The compiler converts it to u16 access while the verifier cgroup_dev_is_valid_access rejects any non u32 access. This patch permits the field access_type to be accessible with type u16 and u8 as well.
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| @@ -1012,7 +1012,8 @@ struct bpf_perf_event_value { · 1011 unmodified lines | ||
| 1012 | 1012 | #define BPF_DEVCG_DEV_CHAR (1ULL << 1) |
| 1013 | 1013 | |
| 1014 | 1014 | struct bpf_cgroup_dev_ctx { |
| 1015 | − __u32 access_type; /* (access << 16) | type */ | |
| 1015 | + /* access_type encoded as (BPF_DEVCG_ACC_* << 16) | BPF_DEVCG_DEV_* */ | |
| 1016 | + __u32 access_type; | |
| 1016 | 1017 | __u32 major; |
| 1017 | 1018 | __u32 minor; |
| 1018 | 1019 | }; |